(Color online) DSC curves of as-quenched glasses. T g denotes the glass transition temperature. The arrow means that the second crystallization peak moves to low temperature with high Yb concentration.
(Color online) Absorption spectra of GGC glasses with different doping concentrations.
(Color online) Excitation spectra of GGC glasses with different doping concentrations monitored at 990 nm.
(Color online) (a) Emission spectra of GGC glasses with different doping concentrations under excitation at 523 nm, including the emission spectrum of the Er0.3Yb0.1 glass after 10 h annealing at T g . The emission peaks show both the features of the Yb3+ and Er3+ emissions. (b) Energy-level diagram of Er3+ and Yb3+, showing the downconversion process between Er3+ and Yb3+ ions with excitation at 523 nm. The energy of energy levels is determined by absorption spectra.
(Color online) (a) Emission spectra of GGC glasses with different doping concentrations under excitation of Yb3+ ions at 458 nm. The inset depicts the same emission spectra that are normalized to the Yb3+ concentration. (b) Scheme demonstrating the position of the energy levels of Yb2+ ions relative to the bandgap of host material. E CT is the charge transfer energy of Yb3+, which approximates E Vf , the energy difference between the top of the valence band of the host material and the 4f 14 ground state of Yb2+. E fd is the energy difference between the ground state of 4f 14 and 4f 135d 1 configuration of Yb2+.25
(Color online) (a) Absorption spectra, and (b) luminescence spectra of the Yb0.3 glass before and after 20-h annealing at 380 °C under ambient condition and vacuum.
(Color online) Decay curves of GGC glasses with different doping concentrations. (a) Decay curves of the 550-nm emission with 523-nm excitation, showing the 4S3/2-level lifetime of Er3+. (b) Decay curves of the 990-nm emission with excitation at 523 nm and 458 nm. The dashed lines are the fitting curves fitted by the double exponential function.
Glass transition temperature T g and crystallization temperature T x (the peak at higher temperature) of as-quenched glasses obtained from DSC curves with accuracy ±2 °C, density ρ, and refractive index n at 990 nm of the glasses.
Absorption cross section of the 4I15/2→2H11/2 transition of Er3+ and absorption edge of the glasses (defined by α = 10/cm).
Lifetimes of the energy levels of Er3+ and Yb3+ in GGC glasses obtained from decay curves. Decay curves of the 990-nm emission with excitation at 523 nm are fitted by the double exponential function. For the others, average lifetimes are obtained. Radiative lifetimes are calculated from the absorption spectra by Eq. (6).27
Quantum yield of the glasses measured by using an integrating sphere under excitation at 523 nm. The quantum yield of emission below 700 nm is directly measured, whereas the other two are calculated from the quantum yield of emission below 700 nm and the relative intensity of emissions in the infrared and in the visible ranges.
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